Effluents from agricultural, aquacultural, many commercial or industrial processes, and sanitary facilities are rich in dissolved nitrogen-containing materials from which valuable fertilizers can be produced. When more than slightly alkaline, such effluents usually emit ammonia and often volatile amines, and re-use of effluent water usually requires their substantial elimination. Frequently other dissolved materials, such as alkaline earth metals, interfere with recovery processes, often accumulating in the system and tending to insoluble deposits restrictive of normal flow--risking inoperation and adding excessively to the cost of the overall operations.
Aluminosilicates are known as ion-exchange media in effecting separation and recovery of dissolved materials from such effluents or wastewaters generally. Aluminosilicate minerals occur in many geographical locations and include prominently for present purposes zeolites, such as chabazite, clinoptilolite, erionite, mordenite, and phillipsite; and layered clay minerals, such as vermiculites and smectites.
The foregoing minerals are hydrated mixed aluminosilicates, with compositions determined largely by the available constituents when they were formed, resulting in diverse crystalline structures. Synthetic aluminosilicates have been produced with more controlled compositions, and often are designated by a letter (e.g., "F", "X") appended to "zeolite." Whether produced under laboratory conditions or in mineral deposits, aluminosilicates range widely in composition, often including alkali metals, such as sodium and potassium, and/or alkaline earth metals, such as magnesium and calcium, and also iron, for example. Their identification, as well as their properties, can vary widely, depending upon their characteristics of interest. The present interest tends to focus upon composition and arrangement of accessible surfaces and sites important to ion-exchange.
Many, if not all or most, aluminosilicates have a characteristic affinity for cations (or anions), which they capture or "take up" in what is considered to be chiefly, but not necessarily exclusively, a surface phenomenon of adsorbing, and may also be partly a solution phenomenon of absorbing, and/or other micromolecular phenomena--and often called just "sorbing" or "sorption," "taking up" or "uptake," or simply "affinity"--which usually differs for dissimilar ions.
Selected aluminosilicates enable ammonium ion and various metal ions to be separated from wastewaters, as disclosed by Weber in U.S. Pat. No. 4,522,727, for example. Preferential zeolitic separation of ammonium (plus heavy metals) from alkali metal ions in solution is taught by Hagiwara and Uchida, using a modified mordenite (zeoharb) in "Ion-Exchange Reactions of Processed Zeolite and Its Applications to the Removal of Ammonia-Nitrogen in Wastes" (at pp. 463-470) in Natural Zeolites, etc., International Conference 1976, published by Pergamon in 1978. Breck in U.S. Pat. No. 3,723,308 characterizes an artificial zeolite (F) as useful to remove ammonium without removing so much alkali or alkaline earth metals as may occur with natural zeolites. So far, however, an effective low-cost remedy for metallic contamination in aluminosilicate recovery of ionic nitrogen materials has been lacking--though badly needed. My invention addresses that need and provides an efficacious and altogether unexpected remedy.